The present invention relates to an electrically-driven vapor compression system which chills a liquid circulated through a garment to provide cooling for an individual or supplied to temperature sensitive hardware devices and is operable on vehicles and other field devices where only direct current (DC) electrical power is available. The present invention also relates to an electrically-driven system which heats a circulated liquid through a garment to supply heat to the individual.
There are many ways to cool and/or heat an individual exposed to uncomfortable ambient temperatures (i.e., cold or hot temperatures). Generally, these technologies fall into the categories of passive and active systems. Passive systems include the use of phase-change materials (PCMs), which act as energy storage devices, and adsorption cooling and/or heating systems, which use the endothermic/exothermic adsorption/desorption of a gas on a chemical or physical adsorbent to supply or absorb heat from the body. Active systems include active refrigeration systems using external power to mechanically cool the individual, and active heating systems using external power to supply heat to the individual.
In the past, cooling technologies adapted for individuals have used a PCM which melts to provide a constant-temperature heat sink for absorption of body heat. A PCM can also be used for heating, in where the PCM freezes at a constant temperature, providing a constant temperature heat source for supplying heat to the body. Although this approach works quite well, the weight penalty of this technology becomes prohibitive for cooling times greater than one to two hours. After the PCM is completely melted or frozen, this process must be reversed to regenerate the PCM for another use cycle. Thus, during this regeneration process, additional PCMs must be available to continue supplying the cooling/heating requirement, or the individual must cease the activity requiring cooling or heating. Regeneration and resupply of the PCM is not always practical, especially if the individual requiring cooling/heating is in the field.
Adsorption cooling and/or heating systems can have many different configurations, but typically utilize the endothermic desorption and exothermic adsorption of a vapor on an adsorbent bed to supply the cooling or heating. These systems also have weight and/or operational drawbacks. Once the adsorbent has reached its adsorption capacity, the adsorbent must be regenerated by driving off the adsorbed vapor (typically using heat), or the adsorbent must be replaced by new adsorbent. During this time period, the required cooling or heating must be supplied by a second (dual) system, or the individual must cease the activity requiring cooling or heating. Also, a regeneration system must be available. These characteristics present a significant weight penalty problem. Also, if the adsorbent is replaced, a supply of new adsorbent must be available and the spent adsorbent must be disposed of.
Active cooling/heating systems are practical only if the individual requiring the heating or cooling has access to power, such as on a motorized vehicle. For cooling, active refrigeration using vapor-compression technology has proven to be suitable. This technology uses a refrigeration-type compressor system to provide cooling; the compressor can be powered, for example, by combustion of fuel, batteries, or tethered external power. These systems have serious drawbacks, however. Compressors driven by fuel combustion are not hermetically sealed because of the shaft seal, and will lose refrigerant from this seal. From an environmental perspective, the loss of even HFC refrigerants into the environment is becoming more unacceptable. Compressors driven by batteries typically have DC motors with brushes to power the compressor. Because the sparks from DC motor brushes can cause degradation to the refrigerant and lubricant, these DC motor compressors cannot be hermetically sealed for this purpose, but are belt-driven or otherwise drive so as to require a shaft seal that will result in refrigerant leakage and increased maintenance. Compressors driven by tethered external power severely limit the portability of the system.
Active refrigeration systems using vapor-compression technology typically condition air and supply it to the individual by cooling the air surrounding the individual. Although these systems work well, they have several drawbacks for use by individuals who require heating or cooling in conditions where heating or cooling the air is not practical. Examples are individuals working in conditions that are open to the ambient atmosphere. Obviously, heating or cooling air which is open to the ambient is not practical due to the significant loss of the energy to the ambient. Also, because the individual breathes the air, filtration is typically required to remove particles, dust, and contaminants, and in military applications, to remove chemical or biological contaminants.
Systems which cool water which is then supplied to the wearer are also known in the art. In such systems, the wearer is cooled by direct contact heat transfer with a garment (vest, pants, cap, etc.) which contains flexible plumbing lines or a bladder incorporated into the garment. A chilled liquid, typically water/antifreeze solution, is pumped through this garment and thereby cools the wearer. It is also known in the art to use thermoelectric devices to cool the liquid which is supplied to the wearer. For heating, electrical heating systems can be used to heat the air surrounding the individual or heat a liquid that is supplied to the individual. Alternatively, heat resulting directly or indirectly from fuel combustion can be used to heat the air or liquid surrounding the individual. The use of thermoelectric devices to provide cooling has several drawbacks. First, thermoelectric devices are inherently inefficient and require considerable amounts of power to provide cooling or heating. Second, the reliability and life of thermoelectric devices is a cause for concern.
It is an object of the present invention to provide an electrically-driven, portable apparatus which produces the desired cooling or heating of an individual working in uncomfortable ambient conditions with access to DC power. Cooling is accomplished using vapor compression refrigeration to cool a circulating liquid loop in thermal communication with the body. The system is operable on vehicles or other field devices where electric power is available and portability is essential. The unit is thus configured with an inverter to provide the required alternating current (AC) power to the compressor. The system can also be configured to provide heat to the body by supplying heated liquid instead of cooled liquid. The cool liquid can also be directed to cold plates to cool avionics or other temperature sensitive electronics or hardware.